| dc.description.abstract | Wildlife Ranching and Research Ltd., Athi River (WRR)is a privately
owned mixed game and cattle ranch, with the aim of demonstrating the
environmental and economic viabi lity, as well as social acceptabi Iity of
game ranching. The field work for this research was carried out at WRR
between October f 986 and September 1987. The emphasis was on
economically important species.
Monthly total ground counts made it possible to evaluate levels of
harvesting that could be accommodated by Grant's gazelle, kongoni and
wi ldebeest. Wildebeest and kongoni could accommodate 32.6%and 14.0%
average annual offtake rates, respectively without the population
decl ining. Grant's gazelle, on the _~therhand, could only accommodate
0.05% annual offtake rate. The highly skewed sex ratio in favour of
females was only partly responsible for the low recruitment in this
species. An unknown mortality factor was considered responsible for the
major part of the low recruitment value. Ground counts carried out in the
wet season were more accurate than the ones carried out in the dry season
for Thomson's gazelle, but not for Grant's gazelle and kongoni. Total
ground counts were more accurate than aerial counts when applied to the
small antelopes, i.e Thomson's and Grant's gazelles and impala combined.
III
No significant differences could be detected between resutts of the- two
methods when applied to the WRRungulate community as a whole. Total
ground counts were recommended as the counting method that best suits
the WRRsituation.
Results of road counts were disappointing. The results exhibited high
variations, and two species, i.e. Thomson's gazelle and wildebeest were
found to prefer the road side, resulting in overestimated population sizes.
Ageing and sexing in the field indicated that Thomson's andGrant's
gazelles, and kongoni breed throughout the year with possible birth peaks
in the cases of Thomson's gazelle and kongoni.
A correction factor was used when calculating the incidence of
pregnancy in wildebeest for the bias resulting from WRRharvesting
strategy of not harvesting pregnant and lactating females. The correction
factor could not be extended to the other species. Equations describing
the rate of foetal growth in wildebeest were given. Environmental
factors affecting rate of foetal growth, variation in the rate of growth and
the timing of the mating season were discussed. It was argued that a
harvesting strategy of avoiding the killing of pregnant and lactating
females may introduce artificial selective pressures that tend to increase
the birth rate. Rates of pregnancy were low in young kongoni and
wildebeest and high inold ones. Recommendations were suggested
related to harvesting timing of the different age and sex classes of the
different species.
Subjective age classes based on eruption sequence and wear pattern
of the maxillary molars provided an accurate ageing criterion up to the age
of 28 months in the case of wildebeest. . Crown heights exhibited high
variation in animals of the same age. The linear regression model
provided a better fit than the exponential to the pattern of decrease of
crown heights with age. | en |
